Update Dependabot config file

Created by: dependabot-preview[bot]

👋 Dependabot is moving natively into GitHub! This pull request updates your config file to the new syntax. When you merge this pull request, we'll swap out dependabot-preview (me) for a new dependabot app, and you'll be all set!

With this change, you'll now use the Dependabot page in GitHub, rather than the Dependabot dashboard, to monitor your version updates. Dependabot is now configured exclusively using config files.

If you've got any questions or feedback for us, please let us know by creating an issue in the dependabot/feedback repository.

Learn more about the relaunch of Dependabot

Please note that regular @dependabot commands do not work on this pull request.

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